There’s an interesting study in this month’s Journal of Applied Physiology about the link between mental fatigue and physical endurance. In a nutshell: “When participants performed a mentally fatiguing task prior to a difficult exercise test, they reached exhaustion more quickly than when they did the same exercise when mentally rested.”

This is a topic I’ve thought a lot about, in part because my occupation is so physically undemanding. I typically spend the day sitting in front of my computer, chatting on the phone, and reading. But if I try to do a hard running workout at the end of a day where I’ve been filing a story on deadline, I STINK! My performance really suffers compared to days when I’ve just been reading or researching. But I don’t get a lot of sympathy from my training partners when I say, “I’m exhausted, I was really typing hard today.”

I had thought it might have something to do with stress hormones, but the researchers (from Bangor University in Wales) suggest another mechanism. Apparently, concentrating hard requires the anterior cingulate cortex region of the brain. Studies have found that rats with a lesion in that area are unable to work as hard for a reward as normal rats — so it may be that our ability to accurately gauge physical effort is put out of whack by too much hard thinking.

This is also another clue that our physical performance limits are almost always mental rather than physical. What we perceive as our bodies reaching their outer limits may, in many cases, just be case of frazzled nerve endings in the anterior cingulate cortex…

Blah. I have a sore throat, a bit of congestion, and I’ve been feeling crappy for a couple of days. So should I exercise or not? Nobody really knows. A few months ago, Gina Kolata wrote an interesting article in the New York Times on this question. A couple of studies done a decade ago suggest that a head cold won’t hurt your capacity to exercise (though you may feel more tired), and exercise won’t speed up or slow down your recovery (though it may make you feel better). Other than that, we’re all just guessing.

Me, I took yesterday off and hoped that would be enough. Then I went for a short jog this morning, but cut it short when I felt worse than I expected. Cliche though it is, listening to your body is probably the best we can do for now. If you start feeling better as you get into it, that’s great; if you feel worse, cut your losses.

Wow, research moves pretty quickly. Just a few hours after posting about the lack of good evidence that running helps bone density…presto! I get a press release about an article by University of Missouri researchers in the current issue of the Journal of Strength and Conditioning Research about how great running is for bone density. You can read the press release here:

In the study, the researchers determined the effects of long-term running, cycling, and resistance training on whole-body and regional BMD [bone mineral density], taking into account the effects of body weight and composition, in men ages 19 to 45. After adjusting for differences in lean body mass, the researchers found that runners had greater spine BMD than cyclists.

This still doesn’t tell us explicitly about how activities like elliptical training, which are weight-bearing but not high-impact, affect bone density. The University of Missouri researchers seem pretty convinced that the jarring action of running (or jumping around by playing basketball, for example) helps bone density. The question is, how much?

I feel that the fitness community has done a great disservice to the average person. One of the most important factors with respect to avoiding osteoporosis is high impact activities… The difference between running and the use of non-impact machines is great when taking into the long term implications on bone density.